Barton Highway is closed in both directions at Wallaroo (north of Canberra) due to a serious crash involving a truck and two cars.
The highway is closed between Victoria Street and Spring Range Road.
Southbound motorists can divert via Murrumbateman Road, Sutton Road and Federal Highway.
The northbound diversion is the same in reverse.
Heavy vehicles can divert via Hume Highway and Federal Highway.
Emergency services including a medical helicopter are on site.
Motorists should exercise caution and allow extra travel time.
For the latest traffic information, download the Live Traffic NSW app, visit www.livetraffic.com or call 132 701